As illustrated in FIG. 1, a traditional outdoor luminaire 10, or lighting fixture, generally includes a pole 12, a light source 14, and perhaps a mounting arm 16 that is used to affix the light source 14 at or near the top of the pole 12. Conventional light sources 14 employ a metal halide, high-pressure sodium, plasma, and induction technology. These types of light sources 14 do not render colors well and many generate high amounts of heat relative to the amount of light produced. Further, luminaires 10 that employ these types of light sources 14 do not evenly light up the target coverage area, such as a roadway or parking lot.
Because the intensity of light falls off in a manner inversely proportional to the square of the distance traveled, higher intensity light is required to equally illuminate longer distances. Assuming the light source 14 is mounted at a height x above the target coverage area, the distance from the light source 14 to the target coverage area is 1.15× at 30 degrees and 2× at 60 degrees. To maintain a relatively uniform illumination of the target coverage area, the light source 14 would have to project 54% more light at 30 degrees than it would directly below the light source 14 (0 degrees). At 60 degrees, the light source 14 would have to project 700% more light than it would directly below the light source 14. Unfortunately, these types of light sources 14 are not only not capable of projecting light in this manner, they often are not capable of projecting the same amount of light at higher angles than they are at lower angles. As such, a substantially uniformly lit target coverage area is virtually impossible with traditional luminaires 10.
Another issue with traditional luminaires 10 is their expense, and in particular the expense of the poles 12. Given the heights of the poles 12 and the mass and surface area associated with the conventional light sources 14 and mounting arms 16, the poles 12 must be substantial to handle normal environmental forces, such as wind, snow and ice. Wind is particularly problematic because the lateral forces imparted by the wind on the light source 14 are effectively multiplied by the mass of the light source 14 and the height of the pole 12 to create rather large moments M1 at the base of the pole 12. Given these substantial forces, the poles 12 must be very robust, and very robust poles 12 are expensive. In most scenarios, the cost of the poles 12 greatly exceeds that of the light sources 14.